Communication networks with two-wire connections (twisted pair cables) are widespread and are also used in building automation for connecting actuators and sensors in a building. In the case of the standardized bus system KNX Twisted Pair (KNX TP), a bus line supplies bus subscribers with data and also with the required operating voltage. Communication networks having two-wire connections are used at field level in automation, control and regulatory, reading, measuring or operator control, and information systems.
In various applications, inexpensive communication networks (field buses) having complex tree structures and great extent, to which many network nodes (e.g. field devices) can be connected, are needed at the field level. For the cabling, simple inexpensive two-wire lines that require no active components at the junctions are usually used. The frequency response of such two-wire lines shows a distinct increase in the damping on the basis of the line lengths and the frequency. The damping produces a decrease in the signal level and hence in the transmission quality in the communication network. Therefore, known field buses (e.g. KNX TP (Twisted Pair)) can be operated only at low data rates (typically 10 kbit/s for a network extent in the region of 1000 m).
Manually setting terminating impedances to reduce the damping and reflections for the network nodes requires a high level of planning and commissioning complexity and is prone to error. The Japanese patent application JP2006074431A discloses a method for regulating terminating circuits, e.g. impedances, in a network, which requires a complex transceiver technology for sending and receiving.